The present invention pertains to a face mask that has a filter element associated with an exhalation valve. The filter element allows the face mask to remove contaminants from the exhale flow stream.
Face masks that have been designed to protect the wearer are commonly referred to as xe2x80x9crespiratorsxe2x80x9d, whereas masks that have been designed primarily with the second scenario in mindxe2x80x94namely, to protect other persons and thingsxe2x80x94are generally referred to as xe2x80x9cface masksxe2x80x9d or simply xe2x80x9cmasksxe2x80x9d.
A surgical mask is a good example of a face mask that frequently does not qualify as a respirator. Some surgical masks are loose fitting face masks, designed primarily to protect other persons from contaminants that are expelled by the wearer. Substances that are expelled from a wearer""s mouth are often aerosols, which generally contain suspensions of fine solids or liquid particles in gas. Surgical masks are quite capable of filtering these particles. U.S. Pat. No. 3,613,678 to Mayhew discloses an example of a loose fitting surgical mask.
Masks that do not seal about the face, such as some known surgical masks, typically do not possess an exhalation valve to purge exhaled air from the mask interior. The masks sometimes are loose fitting to allow exhaled air to easily escape from the mask""s sides so that the wearer does not feel discomfort, particularly when breathing heavily. Because these masks are loose fitting, however, they may not fully protect the wearer from inhaling contaminants or from being exposed to fluid splashes. In view of the various contaminants that are present in hospitals, and the many pathogens that exist in bodily fluids, the loose-fitting feature is a notable drawback for such surgical masks. Additionally, masks that do not seal about the face are known to allow exhaled breath to pass around the mask edges, known as xe2x80x9cblow byxe2x80x9d, and such masks would not benefit from having an exhalation valve attached to the mask body.
Face masks also have been designed to provide a tighter, more hermetic fit between the wearer""s face and the mask. Some tightly fitting masks have a non-porous rubber face piece that supports removable or permanently-attached filter cartridges. The face piece also possesses an exhalation valve to purge warm, humid, high-CO2-content, exhaled air from the mask interior. Masks having this construction are commonly referred to more descriptively as respirators. U.S. Pat. No. 5,062,421 to Bums and Reischel discloses an example of such a mask. Commercially available products include the 5000 and 6000 Series(trademark) masks sold by 3M Company, St. Paul, Minn.
Other tightly fitting face masks have a porous mask body that is shaped and adapted to filter inhaled air. Usually these masks are also referred to as respirators and often possess an exhalation valve, which opens under increased internal air pressure when the wearer exhalesxe2x80x94see, for example, U.S. Pat. No. 4,827,924 to Japuntich.
Additional examples of filtering face masks that possess exhalation valves are shown in U.S. Pat. Nos. 5,509,436 and 5,325,892 to Japuntich et. al., U.S. Pat. No. 4,537,189 to Vicenzi, U.S. Pat. No. 4,934,362 to Braun, and U.S. Pat. No. 5,505,197 to Scholey.
Typically, the exhalation valve is protected by a valve coverxe2x80x94see, for example, U.S. Pat. Nos. Des. 347,299 and Des. 347,298xe2x80x94that can protect the valve from physical damage caused, for example, by inadvertent impacts.
Known tightly fitting masks that possess an exhalation valve can prevent the wearer from directly inhaling harmful particles, but the masks have limitations when it comes to protecting other persons or things from being exposed to contaminants expelled by the wearer. When a wearer exhales, the exhalation valve is open to the ambient air, and this temporary opening provides a conduit from the wearer""s mouth and nose to the mask exterior. The temporary opening can allow aerosol particles generated by the wearer to pass from the mask interior to the outside. Conversely, projectiles such as splash fluids may pass from outside the mask to its interior through the temporary opening.
In many applications, especially in surgery and clean rooms, the open conduit that the exhalation valve temporarily provides could possibly lead to infection of a patient or contamination of a precision part. The Association of Operating Room Nurses has recommended that masks be 95 percent efficient in retaining expelled viable particles. Proposed Recommended Practice for OR Wearing Apparel, AORN JOURNAL, v. 33, n. 1, pp. 100-104, 101 (January 1981); see also D. Vesley et al., Clinical Implications of Surgical Mask Retention Efficiencies for Viable and Total Particles, INFECTIONS IN SURGERY, pp. 531-536, 533 (July 1983). Consequently, face masks that employ exhalation valves are not currently recommended for use in such environments. See e.g., Guidelines for Preventing the Transmission of Mycobacterium Tuberculosis in Health Care Facilities, MORBIDITY AND MORTALITY WEEKLY REPORT, U.S. Dept. Health and Human Services, v. 43, n. RR-13, pp. 34 and 98 (Oct. 28, 1994).
Face masks have been produced that are able to protect both the wearer and nearby persons or objects from contamination. Commercially available products include the 1800(trademark), 1812(trademark), 1838(trademark), 1860(trademark), and 8210(trademark) brand masks sold by the 3M Company. Other examples of masks of this kind are disclosed in U.S. Pat. Nos. 5,307,706 to Kronzer et al., 4,807,619 to Dyrud, and 4,536,440 to Berg. The masks are relatively tightly fitting to prevent gases and liquid contaminants from entering and exiting the interior of the mask at its perimeter, but the masks commonly lack an exhalation valve that allows exhaled air to be quickly purged from the mask interior. Thus, although the masks remove contaminants from the inhale and exhale flow streams and provide splash fluid protection, the masks are generally unable to maximize wearer comfort.
U.S. Pat. No. 5,117,821 to White discloses an example of a mask that removes odor from exhaled air. This mask is used for hunting purposes to prevent the hunted animal from detecting the hunter. This mask has an inhalation valve that permits ambient air to be drawn into the mask""s interior, and it has a purifying canister supported at the wearer""s torso for receiving exhaled air. A long tube directs exhaled air to the remote canister. The device has exhalation valves disposed at the canister""s ends to control passage of purified breath to the atmosphere and to preclude back inhalation of breath from the canister. The canister may contain charcoal particles to remove breath odors.
Although the hunting mask prevents exhaled organic vapors from being transported to the ambient air (and may provide the hunter with an unfair advantage), the mask is not designed to provide a clean air source to the wearer. Nor does it provide an attachment for an intake filter, and it is somewhat cumbersome and would not be practical for other applications.
In view of the above, a filtering face mask is needed that can prevent contaminants from passing from the wearer to the ambient air, that can prevent splash fluids from entering the mask interior, and that allows warm, humid, high-CO2-content air to be quickly purged from the mask""s interior.
This invention affords such a mask, which in brief summary comprises: (a) a mask body; (b) an exhalation valve that is disposed on the mask body and that has at least one orifice that allows exhaled air to pass from an interior gas space to an exterior gas space during an exhalation; and (c) an exhale filter element that does not also serve as an inhale filter element, that comprises a fibrous filter, and that is disposed in the face mask""s exhale flow stream to prevent contaminants from passing from the interior gas space to the exterior gas space with the exhaled air. In one particular embodiment, the exhale filter element is disposed in the exhale flow stream downstream to the valve orifice.
The invention differs from known face masks that possess an exhalation valve in that the invention includes an exhale filter element that can prevent contaminants in the exhale flow stream from passing from the mask""s interior gas space to the exterior gas space. This feature allows the face mask to be particularly beneficial for use in surgical procedures or for use in clean rooms where it would not have been used in the past. Also, unlike some previously known face masks, the invention can be in the form of a tightly-fitting mask that provides the wearer with good protection from airborne contaminants and from splash fluids. And because the inventive face mask possesses an exhalation valve, it can furnish the wearer with good comfort by being able to quickly purge warm, humid, high-CO2-content air from the mask interior. Thus, the invention provides increased comfort to wearers by decreasing temperature, moisture, and carbon dioxide levels within the mask, while at the same time protecting the wearer and preventing particles and other contaminants from passing to the ambient environment.
These and other advantages and features that characterize the invention are illustrated below in the detailed description and accompanying drawings.
In reference to the invention, the following terms are defined as set forth below:
xe2x80x9caerosolxe2x80x9d means a gas that contains suspended particles in solid and/or liquid form;
xe2x80x9cclean airxe2x80x9d means a volume of atmospheric ambient air that has been filtered to remove contaminants;
xe2x80x9ccontaminantsxe2x80x9d means particles and/or other substances that generally may not be considered to be particles (e.g., organic vapors, et cetera) but which may be suspended in air, including air in an exhale flow stream;
xe2x80x9cexhalation valvexe2x80x9d means a valve designed for use on a filtering face mask to open in response to pressure from exhaled air and to remain closed when a wearer inhales and between breaths;
xe2x80x9cexhaled airxe2x80x9d is air that is exhaled by a filtering face mask wearer;
xe2x80x9cexhale filter elementxe2x80x9d means a porous structure through which exhaled air can pass and which is capable of removing contaminants from an exhale flow stream;
xe2x80x9cexhale flow streamxe2x80x9d means the stream of air that passes through an orifice of an exhalation valve;
xe2x80x9cexterior gas spacexe2x80x9d means the ambient atmospheric air space into which exhaled gas enters after passing through the exhalation valve and significantly beyond the face mask;
xe2x80x9cfiltering face maskxe2x80x9d means a mask that covers at least the nose and mouth of a wearer and that is capable of supplying clean air to a wearer;
xe2x80x9cinhale filter elementxe2x80x9d means a porous structure through which inhaled air passes before being inhaled by the wearer so that contaminants and/or particles can be removed therefrom;
xe2x80x9cinterior gas spacexe2x80x9d means the space into which clean air enters before being inhaled by the wearer and into which exhaled air passes before passing through the exhalation valve""s orifice;
xe2x80x9cmask bodyxe2x80x9d means a structure that can fit at least over the nose and mouth of a person and that helps define an interior gas space separated from an exterior gas space;
xe2x80x9cparticlesxe2x80x9d means any liquid and/or solid substance that is capable of being suspended in air, for example, pathogens, bacteria, viruses, mucous, saliva, blood, etc.
xe2x80x9cporous structurexe2x80x9d means a mixture of a volume of solid material and a volume of voids which defines a three-dimensional system of interstitial, tortuous channels through which a gas can pass.